let user = {
  name:'张三',
  birth:'23'
}
observe(user); //观察

function showFirstName() {
  document.querySelector('#firstName').
  textContent = '姓:' + user.name[0]
}

function showLastName() {
  document.querySelector('#lastName').
  textContent = '名:' + user.name.slice(1)
}

function showAge() {
  document.querySelector('#age').
  textContent = '年龄:' + user.birth
}
response(showFirstName)
response(showLastName)
response(showAge)

user.name = "李四"
user.birth = "56"
